Gardaí, the PSNI and Dutch police have made a number of arrests and seized firearms and drugs in a major operation targeting organised crime.
An Irish man (42) was arrested in the Santry area of Dublin and is being held at Blanchardstown Garda Station under the provisions of the Criminal Justice (Drug Trafficking) Act.
According to gardaí, 27 firearms were seized in the operation, including four machine pistols, a quantity of various types of ammunition and firearm accessories, including silencers.
In addition, 20kg of heroin, estimated to be worth over €4 million, and 10kg of cannabis were recovered.
It is understood the man was detained shortly before 4pm today following a surveillance operation by armed gardai who followed him as he drove to an undisclosed location in Santry.
Officers then intervened as he got out of the vehicle and found the weapons and drugs packed inside. Gardaí said more arrests could follow.
In the North, the PSNI said one man (34) from the Republic was arrested in Belfast and that a number of firearms were seized. The man is being questioned in the Antrim Serious Crime Suite, a spokesman said.
It is believed the operation, codenamed Bench, has been going on for between four and six months.
Garda Commissioner Fachtna Murphy welcomed the success of the operation and the co-operation its entailed over three jurisdictions.
"We believe that this operation has made significant inroads into an international organised crime gang involved on a large scale in the importation and distribution of drugs and firearms into Ireland and the United Kingdom."
The operation was assisted by Customs in both the Republic and the United Kingdom.
Det Supt Essie Adair added: "This is a significant operation targeting those involved in organised crime in Northern Ireland, the Republic of Ireland and Europe."
"We believe that this operation has disrupted a major organised crime gang. Those involved in these types of crimes are living off the backs of communities and leaving misery and despair in their wake. Today's operation is extremely significant."
Det Supt Adair said the investigation had been ongoing for some time and had involved close liaison with colleagues in the Garda and Dutch police revenue services on both sides of the Border.
The Minister for Justice, Dermot Ahern, congratulated the Garda.
"On behalf of the Government I want to congratulate the Garda Commissioner and his Officers, together with international police forces, whose successful intelligence led approach has resulted in a highly significant capture of a considerable quantity of illegal drugs and firearms this afternoon."